Photoelectric conversion device, glass composition for coating silicon, and insulating coating in contact with silicon

ABSTRACT

A photoelectric conversion device is provided, which comprises: a substrate serving as an electrode; numerous crystalline semiconductor particles containing a first conductivity-type impurity deposited on the substrate to join thereto; an insulator provided among the crystalline semiconductor particles; and a semiconductor layer containing an impurity of the opposite conductivity-type to which another electrode is connected, which semiconductor layer being provided over the crystalline semiconductor particles, wherein the crystalline semiconductor particles comprise silicon, and the insulator comprises a glass material which contains at least 1 wt % and at most 20 wt % tin oxide. By this arrangement, it is possible to form a good insulator capable of filling spaces among the crystalline semiconductor particles and preventing defects such as cracking, bubbling and abnormal deposition from occurring, and consequently to provide a photoelectric conversion device with high reliability at low cost.

[0001] This application is based on applications Nos. 2001-195878,2001-224634, and 2001-257608 filed in Japan, the content of which isincorporated hereinto by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a photoelectric device usingnumerous crystalline semiconductor particles. This photoelectricconversion device is utilized suitably in solar cells.

[0004] The present invention also relates to a glass composition forcoating silicon that is used for protecting a part of or the entiresurface of silicon or for insulation between electrodes.

[0005] The present invention also relates to an insulating coating thatis formed in a silicon semiconductor device and in contact with thesilicon.

[0006] 2. Description of the Related Art

[0007] (A) Advent of a next-generation, low-cost solar cell that allowsthe amount of the raw material, silicon, to be small has been eagerlyawaited.

[0008] Conventional photoelectric devices in which crystallinesemiconductor particles are used are shown in FIGS. 4 to 6.

[0009]FIG. 4 illustrates a structure disclosed in Japanese UnexaminedPatent Publication (Kokai) No. Showa 61-124179. There is disclosed aphotoelectric conversion device in which a first aluminum foil 10 isformed with apertures into which silicon balls 2 each having a n-typesurface layer 9 formed on the surface of a p-type ball are inserted. Theportions of the n-type surface layers 9 that have penetrated the backsurface of the first aluminum foil 10 are removed, and an oxide layer 3is formed on the back surface of the first aluminum foil 10. Portions ofthe oxide layer 3 that cover the silicon balls are removed, and then asecond aluminum foil 8 is formed so as to join to the silicon balls 2.

[0010]FIG. 5 illustrates a structure disclosed in Japanese PatentPublication No. 2641800. There is disclosed a photoelectric conversiondevice in which a low melting-point metal layer 11 such as a tin layeris formed on a substrate 1. Crystalline semiconductor particles 2 offirst conductivity-type are deposited on the low melting-point metallayer 11, and an amorphous semiconductor layer 7 of secondconductivity-type is formed on the crystalline semiconductor particles 2with an insulating layer 3 interposed between the low melting-pointmetal layer 11 and the amorphous semiconductor layer 7.

[0011]FIG. 6 illustrates a structure disclosed in Japanese ExaminedPatent Publication No. H08-34177. There is disclosed a method in which ahigh melting-point metal layer 12, a low melting-point layer 11 and finecrystalline semiconductor grains 13 are successively deposited on asubstrate 1, and the fine crystalline semiconductor grains 13 aremelted, saturated, and gradually cooled so that the semiconductor isgrown by liquid-phase epitaxial growth, thereby forming the finecrystalline semiconductor grains 13 into a polycrystalline thin film.Incidentally, in FIG. 6, the numeral 14 denotes a polycrystalline oramorphous semiconductor layer of the opposite conductivity type, and thenumeral 6 denotes a transparent conductive film.

[0012] In the photoelectric conversion device shown in FIG. 4, however,since the first aluminum foil 10 is formed with apertures into which thesilicon balls 2 are pressed and inserted so as to join the n-type layers9 of the silicon balls 2 and the aluminum foil together, the siliconballs 2 are required to have a uniform diameter. The manufacturing costis therefore high. Also, since the temperature used for joining is lowerthan 577° C., which is the eutectic temperature of aluminum and silicon,the joining tends to be unstable.

[0013] In the photoelectric conversion device shown in FIG. 5, since theinsulator 3 is formed after the crystalline semiconductor particles havebeen fixed on the low melting-point metal layer 11, the insulator 3 isformed not only on the low melting-point metal layer 11 but also on thecrystalline semiconductor particles 2. Therefore, the insulator 3 on thecrystalline semiconductor particles 2 needs to be removed before theamorphous semiconductor layer 7 is formed, which causes the number ofprocesses to increase. Since the thickness of the amorphoussemiconductor layer 7 needs to be small taking the great lightabsorption thereof into account. When the thickness of the amorphoussemiconductor layer 7 is small, the tolerance to defects also becomessmall necessitating stricter management of the cleaning process and theproduction environment. As a result, the manufacturing cost is high.

[0014] In the photoelectric conversion device shown in FIG. 6, since thelow melting-point metal layer 11 is mixed into the firstconductivity-type liquid-phase epitaxial polycrystalline layer 13, theperformance of the solar cell is degraded. And due to the absence ofinsulator, current leakage occurs between the upper electrode 6 and thelower electrode 12.

[0015] In addition, it has been known that when conventional glasscompositions are employed for the insulator in conventionalphotoelectric conversion devices, bubbling occurs due to its reaction tothe crystalline semiconductor particles, and microcracks are generatedduring reliability tests.

[0016] It is a primary object of the present invention to provide aphotoelectric conversion device with high conversion efficiency that canbe manufactured at low cost.

[0017] (B) In today's age of intense information, information andcommunications technologies have rapidly been developing. Along withthis trend, the demand for silicon semiconductor devices for use in MPUsand memories has been sharply on the rise. In addition, with theincreasing consciousness for the environment, applications of siliconsemiconductor devices other than information and communicationsequipment, such as solar cells, have been increasing fast.

[0018] In order to prevent errors and secure long-time reliability, thesilicon is covered with an insulating coating in such semiconductordevices. By covering the silicon with an insulating coating, the siliconis protected from water and dust and insulation is provided between theelectrodes.

[0019] For insulating coatings used for protecting silicon in opticalsemiconductor devices such as optical sensors and solar cells orinsulating coatings for insulation between the electrodes in suchoptical semiconductor devices, transparency is required in addition tothe insulation property and sealing property.

[0020] For the purpose of silicon protection, organic resin is employedfor protection and sealing in applications in which the demand forreliability is relatively low. In applications for which highreliability is required, the insulating coating needs to be formed byusing glass.

[0021] Generally, the insulating coatings made from glass are formed bycovering silicon with glass paste, which is obtained by mixingparticulate glass, organic binder, and solvent together, by a knownprinting method, a dispensing process, dipping or spin-coating, andthereafter performing a heat treatment to soften and fluidize the glass.The glass which has been conventionally used for forming insulatingcoatings to cover silicon is low softening-point glass composed mainlyof PbO so that influence on the semiconductor device by heat isminimized.

[0022] However, since the PbO content needs to be large in order tolower the softening point and glass transition point, PbO-based lowsoftening-point glass has a thermal expansion coefficient as high as80×10⁻⁷/° C. at temperatures 40 to 400° C. When PbO-based lowsoftening-point glass with such a high thermal expansion coefficient isemployed for protection and insulation in silicon semiconductor deviceswith thermal expansion coefficients as low as 30×10⁻⁷/° C. to 45×10⁻⁷/°C., especially in large scale silicon semiconductor devices or solarcells with greater areas, due to thermal stress accompanying the ON/OFFswitching of the semiconductor device and changes in the environment ofuse, cracks are generated in the glass and silicon and peeling occurs atthe interfaces.

[0023] In order to lower the thermal expansion coefficient of thePbO-based low softening-point glass, adding a filler with a low thermalexpansion coefficient is a general practice. However, this measurecauses the insulating coating to have turbidity and loose transparency.

[0024] On the other hand, when the PbO content is reduced, although thethermal expansion coefficient is lowered by which the inconvenience dueto the thermal stress mentioned above can be avoided, the softeningpoint and glass transition point rise in most cases. This increasesdamage by heat to the silicon semiconductor devices.

[0025] In addition, using PbO is very unfavorable considering theadverse effects on the environment. The trend toward Pb-freemanufacturing is accelerating in all industry fields. Likewise, thedemand for Pb-free insulating coatings for silicon is sharply on therise.

[0026] As discussed so far, there has been a surge in demand forlead-free glass powder with a low glass transition point and a lowthermal expansion coefficient. One example of such glass is the glassdisclosed in Japanese Unexamined Patent Publication No. H09-278482,which is composed mainly of B₂O₃—ZnO.

[0027] However, when an insulating coating is formed by using theB₂O₃—ZnO-based glass disclosed in the Japanese Unexamined PatentPublication No. H09-278482 above, the following problems arise: thesilicon and glass react to each other making the use of the siliconsemiconductor device impossible; the resultant insulating coating failsto obtain adequate sealing property because of great defectsaccompanying generation of bubbles; the insulating coating fails toobtain transparency.

[0028] Furthermore, due to crystallization of the B₂O₃—ZnO-based glassduring the heat treatment, the insulating coating cannot be formed withtransparency.

[0029] The present inventors discovered that, by lowering the thermalexpansion coefficient and glass transition point of B₂O₃—ZnO-basedglass, and by adding SiO₂ thereto, it is possible to suppress thereaction between glass and silicon, prevent generation of bubbles, andprevent crystallization at the same time. The present invention has beenthus accomplished.

[0030] It is an object of the present invention to provide a glasscomposition for coating silicon that is capable of forming a transparentinsulating coating with long time reliability, which has a low glasstransition point and a low thermal expansion coefficient, and does notcontain lead nor react to silicon, and is not crystallized at thedesired temperature range.

[0031] It is another object of this invention to provide a transparentinsulating coating in contact with silicon with a low glass transitionpoint and a low thermal expansion coefficient, which does not containlead and not react to silicon and is not crystallized at the desiredtemperature range, and has long time reliability.

BRIEF SUMMARY OF THE INVENTION

[0032] (A) A photoelectric conversion device according to the presentinvention comprises: a substrate serving as an electrode; numerouscrystalline semiconductor particles containing a first conductivity-typeimpurity deposited on the substrate to join thereto; an insulatorprovided among the crystalline semiconductor particles; and asemiconductor layer containing an impurity of the oppositeconductivity-type to which another electrode is connected, whichsemiconductor layer being provided over the crystalline semiconductorparticles, wherein the crystalline semiconductor particles comprisesilicon, and the insulator comprises a glass material which contains atleast 1 wt % and at most 20 wt % tin oxide.

[0033] A photoelectric conversion device according to the presentinvention comprises: a substrate serving as an electrode; numerouscrystalline semiconductor particles containing a first conductivity-typeimpurity deposited on the substrate to join thereto; an insulatorprovided among the crystalline semiconductor particles; and asemiconductor layer containing an impurity of the oppositeconductivity-type to which another electrode is connected, whichsemiconductor layer being provided over the crystalline semiconductorparticles, wherein the crystalline semiconductor particles comprisesilicon, and the insulator comprises a glass composition which contains4.2 to 20 wt % tin oxide.

[0034] According to these photoelectric conversion devices, theinsulator comprising the glass material that contains the above-statedamount of tin oxide fills spaces among the crystalline semiconductorparticles and covers the whole exposed surface of the substrate withoutcausing defects.

[0035] Accordingly, occurrence of cracking in the insulator andcrystalline semiconductor particles is prevented, and defects such asbubbling and abnormal deposition can be prevented.

[0036] This allows crystalline semiconductor particles to be producedwith lower grain size precision, the resultant photoelectric conversiondevice therefore yields a larger manufacturing margin permittingmanufacturing thereof at lower manufacturing cost as compared withconventional photoelectric conversion devices.

[0037] Moreover, the presence of the insulator ensures separation of thepositive electrode from the negative electrode. By employing a glassmaterial containing tin oxide for the insulator, the molten glass andthe silicon of the crystalline semiconductor particles are preventedfrom excessively reacting to each other. Low cost manufacturing istherefore realized.

[0038] Accordingly, it is possible to form a good insulator with stablereliability and provide a photoelectric conversion device with highreliability.

[0039] (B) A glass composition for coating silicon according to thepresent invention is substantially free of PbO, and contains B₂O₃, ZnO,and SnO₂, and has a thermal expansion coefficient of 80×10⁻⁷/° C. orless at temperatures from 40 to 400° C. and a glass transition point of550° C. or below.

[0040] An insulating coating in contact with silicon according to thepresent invention comprises a glass composition which is substantiallyfree of PbO, and contains B₂O₃, ZnO, and SnO₂, and has a thermalexpansion coefficient of 80×10⁻⁷/° C. or less at temperatures from 40 to400° C. and a glass transition point of 550° C. or below.

[0041] A method of forming an insulating coating according to thepresent invention comprises the steps of: covering a surface of siliconwith a glass powder which is substantially free of PbO, and containsB₂O₃, ZnO, and SnO₂, and has a thermal expansion coefficient of80×10⁻⁷/° C. or less at temperatures from 40 to 400° C. and a glasstransition point of 550° C. or below; and performing a heat treatment ata temperature of 600° C. or below to soften and fluidize the glasspowder, whereby forming an insulating coating on the silicon.

[0042] A photoelectric conversion device according to the presentinvention comprises silicon therein which is partly or wholly coatedwith an insulating coating comprising a glass composition which issubstantially free of PbO, and contains B₂O₃, ZnO, and SnO₂, and has athermal, expansion coefficient of 80×10⁻⁷/° C. or less at temperaturesof 40 to 400° C. and a glass transition point of 550° C. or below.

[0043] Since the insulating coatings applied on the surface of thesilicon described above have a low glass transition points and lowthermal expansion coefficients, and do not react to the silicon, theycause little bubbling and are not crystallized at the desiredtemperature range. Accordingly, they have transparency as well as longtime reliability.

[0044] The structural details for achieving the objects of thisinvention are now described referring to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIG. 1 is a cross-sectional view showing a photoelectricconversion device according to the present invention.

[0046]FIG. 2 is a cross-sectional view of a photoelectric conversiondevice according to the present invention in which the substrate has atwo-layer structure.

[0047]FIG. 3 shows a schematic cross-section of an optical sensoremploying an insulating coating according to the present invention.

[0048]FIG. 4 is a cross-sectional view of a photoelectric conversiondevice according to a conventional example 1.

[0049]FIG. 5 is a cross-sectional view of a photoelectric conversiondevice according to a conventional example 2.

[0050]FIG. 6 is a cross-sectional view showing a photoelectricconversion device according to a conventional example 3.

DETAILED DESCRIPTION OF THE INVENTION

[0051] <First Embodiment (photoelectric conversion device)>

[0052]FIGS. 1 and 2 are cross-sectional views of photoelectricconversion devices according to the present invention.

[0053]FIG. 1 shows a substrate (an electrode layer) 1, crystallinesemiconductor particle 2, an insulator 3 comprising a glass material, asemiconductor layer 4, a protective layer 5, a conductive layer (anotherelectrode layer) 6, and alloy layers 15 comprising the substrate 1 andthe crystalline semiconductor particles 2.

[0054] The substrate 1 is composed of metal with a melting point higherthan that of aluminum or ceramics. For example, aluminum, an aluminumalloy, iron, an iron alloy such as invar or covar, stainless steel,nickel, alumina or the like is used.

[0055] The substrate 1 may have a two-layer structure consisting of alayer made of a material other than aluminum and an electrode layer 1 amade of aluminum as illustrated in FIG. 2. It is also possible to addone or a plural kinds of elements selected from among silicon,magnesium, manganese, chromium, titanium, nickel, zinc, silver, andcopper to the electrode layer 1 a made of aluminum so that it is keptprevented from excessive melting at the time of joining the crystallinesemiconductor particles 2 thereto. The thickness of the electrode layer1 a is 20 μm or more. When the thickness is less than 20 μm, due to theshortage of thickness, the electrode layer 1 a fails to have sufficientelectrical connection with the crystalline semiconductor particles 2when joined thereto.

[0056] Numerous first conductivity-type crystalline semiconductorparticles 2 are deposited on the substrate 1 or the electrode layer 1 a.The crystalline semiconductor particles 2 comprise Si or Ge, and smallamount of p-type impurity such as B, Al, and Ga, or n-type impurity suchas P and As added thereto.

[0057] The shapes of the semiconductor particles 3 may be polygons,curved surfaces or the like. The particle sizes may be even or uneven.However, uneven particle sizes will be advantageous to make the devicemore economical, because an additional process is necessary in order touniformize the particle sizes. Also, having convex surfaces reduces thedependence on the incident angle of light.

[0058] Preferably, the particle sizes are in the range of 0.2 to 0.8 mm.Using crystalline semiconductor particles with particle sizes exceeding0.8 mm makes no difference in the amount of the semiconductor materialto be used from the amount used in conventional crystal plate typephotoelectric conversion devices, which nullifies the material-savingadvantage of using crystalline semiconductor particles. In addition,crystalline semiconductor particles with diameters less than 0.2 mm aredifficult to be deposited on the substrate 1, which is another problem.More desirably, the particle sizes are in the range of 0.2 to 0.6 mm,considering the amount of silicon to be used.

[0059] A method for depositing numerous crystalline semiconductorparticles 2 on the substrate 1 or the electrode layer 1 a is as follows:a joining-aide layer that functions to bond and fix the crystallinesemiconductor particles 2 to the surface of the substrate 1 is formed onthe substrate 1, and the crystalline semiconductor particles 2 aredeposited thereon, and then extra crystalline semiconductor particles 2are dropped. This makes it possible to deposit the crystallinesemiconductor particles 2 stably and densely on the surface of thesubstrate 1, irrespective of the particle size.

[0060] Subsequently, with a certain amount of load applied to thecrystalline semiconductor particles 2, they are heated at a temperaturehigher than 577° C., which is the eutectic temperature of aluminum inthe substrate 1 or electrode layer 1 a and silicon in the crystallinesemiconductor particles 2. Through this process, the substrate 1 and thecrystalline semiconductor particles 2 can be joined together with thealloy layer 15 comprising the substrate 1 and the crystallinesemiconductor particles 2 in between, while the joining-aide layer isremoved by the heat. At this stage, all of the aluminum contained in thesubstrate 1 or the electrode layer 1 a is contained in the alloy layer15.

[0061] Incidentally, in the first conductivity type regions that are incontact with the alloy layers 15, aluminum, which is the material of thesubstrate 1, is dispersed and forms p+ layers within the crystallinesemiconductor particles 2.

[0062] If formation of conductive diffusion regions p+ is simplyintended for, heating at a temperature below the eutectic temperature ofAl and Si i.e. 577° C. will serve the purpose. However, in such a case,the joining between the substrate 1 and the crystalline semiconductorparticles 2 is so weak that the crystalline semiconductor particlesleave the substrate, failing to maintain the structure as a solar cell.

[0063] The material for the joining-aide layer may be one thatdisappears at temperatures above 300° C. and below the temperature atwhich the substrate 1 and crystalline semiconductor particles 2 arejoined. In cases where the process is performed in an oxidizingatmosphere, organic resin such as butyral resin, methylcellulose,ethylcellulose, polyvinyl alcohol(PVA), or polyethylene glycol (PEG)being dissolved in a solvent may be used. The process for forming thejoining-aide layer may be a screen printing method, the doctor blademethod, spraying, dipping or the like, by which the joining-aide layeris formed on the surface of the substrate 1 with a thickness of 10 to100 μm.

[0064] The insulator 3 is provided for separating the positive electrodefrom the negative electrode and comprises an insulating material. Thematerial may be, for example, a single glass material forlow-temperature firing composed of components arbitrarily selected fromamong SiO₂, B₂O₃, Al₂O₃, CaO, MgO, P₂O₅, Li₂O, SnO, ZnO, Bao, TiO₂ andthe like, or a glass material mixture in which a single glass materialfor low-temperature firing and a filler composed of one or a pluralityof the above listed materials are combined together.

[0065] Powder of the glass material above is formed into paste by usinga solvent or binder and applied over the crystalline semiconductorparticles 2 deposited on the substrate 1, and then it is heated at atemperature below the eutectic temperature of aluminum and silicon, 577°C., by which the glass material is melted to form the insulator 3.

[0066] When the heating temperature exceeds 577° C., the alloy layers 15comprising aluminum and silicon start melting causing the joiningbetween the substrate 1 and crystalline semiconductor particles 2 tobecome unstable. In some cases, due to the crystalline semiconductorparticles 2 leaving the substrate 1, it is impossible to generate aphotoelectric current.

[0067] When a glass material is melted so as to form the insulator 3, ifexcessive reaction occurs between the glass material and the silicon ofthe crystalline semiconductor particles 2, a bubbling phenomenon occurs,creating defects in the insulator, which leads to the problem of currentleakage.

[0068] In order to suppress the reaction between the melted glassmaterial and silicon in the crystalline semiconductor particles 2, tinoxide is added to the glass material. The amount of the addition may beat least 1 wt % and at most 20 w%. When it is less than 1 wt %, bubblingcannot be suppressed, and when it is more than 20 wt %, the softeningpoint of the glass is raised and the glass does not melt at 577° C.,failing to fill spaces among the crystalline semiconductor particles.

[0069] A material having a thermal expansion coefficient of 30×10⁻⁷/° C.to 65×10⁻⁷/° C. at temperatures of 30 to 300° C. is used as the glassmaterial. Thermal expansion coefficients less than 30×10⁻⁷/° C. are sodifferent from the thermal expansion coefficient of the substrate 1,which is the thermal expansion coefficient of aluminum, 240×10⁻⁷/° C.that cracking occurs on the surface of the insulator 3 after theformation thereof. Thermal expansion coefficients more than 65×10⁻⁷/° C.are so different from that of the crystalline semiconductor particles 2,which is, for instance, the thermal expansion coefficient of Si:26×10⁻⁷/° C., that cracking occurs in the crystalline semiconductorparticles 2 and the insulator 3 around them.

[0070] Also, it is necessary that the softening point of the glassmaterial is in a specific range so that the glass material is not meltedor decomposed at the temperature for forming the semiconductor layer.With a softening point above 560° C., the glass material does not meltat temperatures near 577° C., which are the temperatures for joining thesubstrate 1 and crystalline semiconductor particles 2, failing to fillthe spaces among the crystalline semiconductor particles 2. In such acase, the glass material cannot function as an insulator. Accordingly,the range of the softening point is, taking the temperature for formingan amorphous semiconductor layer into consideration, 200 to 560° C.Preferably, the range is 350 to 560° C., when the temperature forforming a semiconductor layer comprising a mixture of amorphous andcrystalline semiconductors is taken into consideration.

[0071] After the insulator is formed, the surfaces of the crystallinesemiconductor particles 2 are cleaned with cleaning liquid containinghydrofluoric acid. At this stage, if the insulator 3 contains a leadcompound, the lead component is reduced into metal lead to be depositedon the surface of the insulator 3, causing current leakage. It istherefore favorable to use a glass material not containing lead oxide.

[0072] Meanwhile, although the description above refers to a method inwhich the insulator 3 is formed after the crystalline semiconductorparticles 2 have been joined to the substrate 1, there is another methodin which the insulator 3 is applied over numerous crystallinesemiconductor particles 2 that have been deposited on the substrate 1,and then they are heated altogether so as to join the crystallinesemiconductor particles 2 to the substrate 1 and form the insulator 3 atthe same time.

[0073] The semiconductor layer 4 comprises, for example, Si. Thesemiconductor layer 4 is formed by a vapor-phase growth method or thelike in which, for example, a phosphorous compound that is a n-typeimpurity or a boric compound that is a p-type impurity is added in smallamount to a silane compound. The semiconductor layer may be ofcrystalline, amorphous, or mixture of crystalline and amorphous. Whenthe light transmittance is taken into consideration, it is preferablethat the layer comprises a crystalline semiconductor or a mixture ofcrystalline and amorphous semiconductors.

[0074] Apart of incident light penetrates the semiconductor layer 4 atareas where the crystalline semiconductor particles 2 are not present,and is reflected by the substrate 1 and directed to the crystallinesemiconductor particles 2. This enables energy of light incident on thewhole photoelectric conversion device to be efficiently transmitted tothe crystalline semiconductor particles 2.

[0075] The conductivity of the semiconductor layer 4 may be, forexample, on the order of 1×10¹⁶ to 1×10²¹ atm/cm³.

[0076] In addition, the semiconductor layer 4 preferably be formed alongthe contours of the convex surfaces of the crystalline semiconductorparticles 2. By forming the semiconductor layer 4 along the convexsurfaces of the crystalline semiconductor particles 2, large areas canbe provided for p-n junctions. Accordingly, carriers generated insidethe crystalline semiconductor particles 2 can be efficiently collected.

[0077] Meanwhile, when the crystalline semiconductor particles 2 to beused are arranged such that each particle has a surface layer containingsmall amount of n-type impurity such as P or As, or p-type impurity suchas B, Al, or Ga, the semiconductor layer 4 may be spared, and theconductive layer 6 is formed directly over the crystalline semiconductorparticles 2.

[0078] On the semiconductor layer 4, the conductive layer 6 (anotherelectrode) is formed. The conductive layer 6 is formed by a film-formingmethod such as the sputtering method or the vapor-phase growth method,or a coating and heating process. The conductive layer 6 is anoxide-based film composed of one or a plurality of compounds selectedfrom among SnO₂, In₂O₃, ITO, ZnO, TiO₂ and the like, or a metal-basedfilm composed of one or a plurality of metals selected from among Ti,Pt, Au and the like. In addition, the conductive layer 6 needs to betransparent so that a part of incident light penetrates the conductivelayer 6 at areas where the crystalline semiconductor particles 2 are notpresent, and is reflected by the substrate 1 and directed to thecrystalline semiconductor particles 2. This enables energy of lightincident on the whole photoelectric conversion device to be efficientlytransmitted to the crystalline semiconductor particles 2. A transparentconductive layer can have the effect of an antireflective film if thethickness is selected for that purpose. In addition, the conductivelayer 6 is formed along the surface of the semiconductor layer 4 oralong the surfaces of the crystalline semiconductor particles 2.Preferably it is formed along the convex contours of the crystallinesemiconductor particles 2. By forming the semiconductor layer 4 alongthe convex surfaces of the crystalline semiconductor particles 2, largeareas can be provided for p-n junctions. Accordingly, carriers generatedinside the crystalline semiconductor particles 2 can be efficientlycollected.

[0079] A protective layer 5 may be formed on the semiconductor layer 4or on the conductive layer 6.

[0080] It is preferable for the protective layer 5 to have theproperties of a transparent dielectric. It is formed by the CVD method,the PVD method or the like, in which, for example, one or a plurality ofmaterials selected from among silicon oxide, cesium oxide, aluminumoxide, silicon nitride, titanium oxide, SiO₂—TiO₂, tantalum oxide,yttrium oxide are used to form a single layer or a combined layer on thesemiconductor layer 4 or on the conductive layer 6. The protective layer5 needs to be a transparent dielectric, because transparency isnecessary for the layer being in contact with the surface where light isincident, and in order to prevent current leakage from occurring betweenthe outside and the semiconductor layer 4 or the conductive layer 6, itneeds to be a dielectric. It is possible to provide the protective layer5 with the function of an antireflective film by optimizing thethickness of the layer for that purpose.

[0081] Moreover, it is also possible to provide a patterned electrodecomprising fingers and bus bars at regular intervals on thesemiconductor layer 4 or on the conductive layer 6 so as to connect thepatterned electrode directly or indirectly to the semiconductor layer 4,thereby lowering the series resistance and consequently improving theconversion efficiency.

[0082] Example

[0083] A substrate formed by attaching a 50 μm thick aluminum alloy ontoa stainless steel by cold pressing process was used. For forming ajoining-aide layer, a butyral resin was dissolved in an organic solventand applied by screen printing or the doctor blade method on thesubstrate.

[0084] On top of them, p-type silicon particles with particle sizes of0.2 to 0.6 mm were supplied several times so that the p-type siliconparticles adhered firmly enough to the joining-aide layer. Then, thesubstrate was tilted to remove extra portion of the p-type siliconparticles. Thereafter, with the p-type silicon particles being pressedby a certain amount of load and kept still, they were heated in theatmospheric air at a temperature above the eutectic temperature ofaluminum and silicon, 577° C., for 5 to 30 minutes, thereby joining thesilicon particles to the aluminum alloy. In order to form an insulatorover the silicon particles, glass particles for low-temperature firingprepared in the form of paste shown in Table 1, which were composed ofSiO₂, B₂O₃, Al₂O₃, Li₂O, SnO₂, ZnO and had average diameters of 0.5 to 5μm were applied over the silicon particles so that the thickness afterfiring was about half the particle size of the silicon particles 2.Then, a heat treatment was carried out at a temperature above theeutectic temperature 577° C. of aluminum and silicon for 5 to 30minutes, thereby forming the insulator 3.

[0085] Through the above-mentioned process, fourteen kinds of sampleswere fabricated by varying the components and contents thereof of theinsulator 3 (Examples 1 to 7, Comparative examples 1 to 7). The numberof each sample was five.

[0086] In example 1 to 7, the content of tin oxide in the glass was atleast 1 wt %, and at most 20 wt %. TABLE 1 Silicon Thermal particle SnO₂PbO expansion Softening size Glass content content coefficient point(mm) composition (wt %) (wt %) (E-7)/° C. (° C.) E1 0.3 SiO₂, B₂O₃, ZnO20 0 58 560 Al₂O₃, Li₂O, SnO₂ E2 0.3 SiO₂, B₂O₃, ZnO 12 0 56 552 Al₂O₃,Li₂O, SnO₂ E3 0.3 SiO₂, B₂O₃, ZnO 5 0 55 540 Al₂O₃, Li₂O, SnO₂ E4 0.3SiO₂, B₂O₃, ZnO 1 0 50 545 Al₂O₃, Li₂O, SnO₂ E5 0.3 SiO₂, B₂O₃, ZnO 5 063 538 Al₂O₃, Li₂O, SnO₂ E6 0.2 SiO₂, B₂O₃, ZnO 5 0 55 540 Al₂O₃, Li₂O,SnO₂ E7 0.6 SiO₂, B₂O₃, ZnO 5 0 55 540 Al₂O₃, Li₂O, SnO₂ C1* 0.3 SiO₂,B₂O₃, ZnO 22 0 60 567 Al₂O₃, Li₂O, SnO₂ C2* 0.3 SiO₂, B₂O₃, ZnO 0 0 51545 Al₂O₃, Li₂O, SnO₂ C3* 0.3 SiO₂, B₂O₃, ZnO 0.5 0 51 545 Al₂O₃, Li₂O,SnO₂ C4* 0.3 SiO₂, B₂O₃, ZnO 5 0 68 537 Al₂O₃, Li₂O, SnO₂ C5* 0.3 SiO₂,B₂O₃, ZnO 5 0 45 570 Al₂O₃, Li₂O, SnO₂ C6* 0.3 SiO₂, B₂O₃, ZnO 5 30  56530 Al₂O₃, Li₂O, SnO₂, PbO C7* 0.3 SiO₂, B₂O₃, ZnO 3 10  58 543 Al₂O₃,Li₂O, SnO₂, PbO

[0087] The states of stress-cracking of the silicon particles 2 and theinsulator 3, and the melting state of the insulator 3 were checked foreach sample fabricated, the results of which are shown in Table 2.Subsequently, the upper surfaces of the p-type silicon particles 2 werecleaned by hydrofluoric acid aqueous solution (HF: pure water=1:100) for2 to 5 minutes, and the appearance was evaluated for each sample, theresults of which are also shown in Table 2.

[0088] Subsequently, a semiconductor layer 4 comprising a mixture ofn-type crystalline silicon and amorphous silicon was formed over thesilicon particles 2 and the insulator 3 to have a thickness of 300 nm,on which a silicon nitride film as a protective layer 5 was formed tohave a thickness of 600 nm. A patterned electrode was formed in theregion where a part of the protective layer 5 had been removed byetching so that it was connected to the semiconductor layer 4 to serveas the other electrode. Light was introduced vertically into thephotoelectric conversion devices fabricated in the above describedmanner and the conversion efficiency was measured for each sample, theresults of which are shown in Table 2. TABLE 2 Appearance afterConversion Melting Crack- Bub- cleaning efficiency Overall state ingbling with HF (%) evaluation E1 ◯ ◯ ◯ ◯ 10.5 ◯ E2 ◯ ◯ ◯ ◯ 10.6 ◯ E3 ◯ ◯◯ ◯ 10.6 ◯ E4 ◯ ◯ ◯ ◯ 10.7 ◯ E5 ◯ ◯ ◯ ◯ 10.8 ◯ E6 ◯ ◯ ◯ ◯ 11.0 ◯ E7 ◯ ◯◯ ◯ 10.4 ◯ C1* X ◯ ◯ ◯ — X C2* ◯ ◯ X ◯ 4.8 X C3* ◯ ◯ X ◯ 5.1 X C4* ◯ X ◯◯ 5.2 X C5* X ◯ ◯ ◯ — X C6* ◯ ◯ ◯ Pb — X deposition C7* ◯ ◯ ◯ Pb — Xdeposition

[0089] In examples 1 to 5, no bubbling was observed in the interfaces ofthe silicon particles 2 and the insulator 3. The insulator 3 was able tofill the spaces among the silicon particles 2.

[0090] In comparative example 1, the insulator 3 did not melt at 577° C.This may be attributable to the high (22 wt %.) tin oxide content in theinsulator 3.

[0091] In comparative examples 2 and 3, bubbling occurred in theinterfaces between the silicon particles 2 and the insulator 3. This maybe explained that due to the low content of tin oxide in the insulator3, which was below 1 wt %, intense reaction occurred between the siliconparticles 2 and the insulator 3.

[0092] In comparative example 4, the thermal expansion coefficient was68×10⁻⁷/° C. Cracking occurred in the silicon particles 2 and theinsulator 3. No cracking was observed in examples 1 to 5. Judging fromthese results, a preferred thermal expansion coefficient is 65×10⁻⁷/° C.or below.

[0093] In comparative example 5, the glass particles did not melt due tothe high softening point of 577° C. In examples 1 to 5, the glassparticles melted and could fill the spaces among the silicon particles2. Judging from these results, a preferred softening point is 560° C. orbelow.

[0094] In comparative examples 6 and 7, PbO was added to the glasscomponents. When cleaning was performed after the formation of theinsulator 3 by using hydrofluoric acid aqueous solution {HF:purewater=1:100} for 2 to 5 minutes, abnormal deposition of metal lead onthe surface of the insulator 3 was observed. Due to excessive currentleakage, measurement of the conversion efficiency was impossible. On theother hand, such abnormal metal deposition was not observed in examples1 to 5, and measurements of conversion efficiency were normallyperformed. Judging from these results, it is preferable not to containlead oxide in the glass material of the insulator 3.

[0095] In examples 6 and 7, the samples were fabricated by varying theparticle size of the silicon particles 2 to 0.2 mm and 0.6 mm. Theobtained conversion efficiencies were similar to those of examples 1 to4.

[0096] Accordingly, it has been verified that a good insulator capableof filling spaces among the silicon particles 2 and preventinggeneration of defects such as cracking, bubbling and abnormal depositioncan be formed by the present invention.

[0097] <Second Embodiment (photoelectric conversion device)>

[0098] The cross sectional view of the photoelectric conversion deviceaccording to this second embodiment is the same as those shown in FIGS.1 and 2. Accordingly, only the elements that are different from thefirst embodiment are described below.

[0099] An insulator 3 is made of an insulating material for separatingthe positive electrode from the negative electrode. It is formed byusing a glass composition for low-temperature firing that is composedmainly of SiO₂, B₂O₃, ZnO and Al₂O₃, and contains SnO₂ or SnO addedthereto and further contains one or more alkali metal oxides such asLi₂O, Na₂O, K₂O and the like. Powder of the glass material above isformed into paste by using a solvent or binder. The paste is appliedover crystalline semiconductor particles 2 deposited on a substrate 1,and then heating is carried out at a temperature below the eutectictemperature 577° C. of aluminum and silicon so as to melt the glassmaterial, thereby forming the insulator 3.

[0100] When the heating temperature exceeds 577° C., the alloy layers 15comprising aluminum and silicon start melting causing the joiningbetween the substrate 1 and crystalline semiconductor particles 2 tobecome unstable. In some cases, due to the crystalline semiconductorparticles 2 leaving the substrate 1, it is impossible to generate aphotoelectric current.

[0101] The compound SnO₂ or SnO that is added to the glass compositionfor forming the insulator 3 is an essential component for suppressingreaction between silicon and B₂O₃—Z_(n)O glass. In cases where SnO₂ orSnO is not contained, due to reaction gas resulted from a reactionbetween glass and silicon, bubbling occurs in the insulator 3,generating great defects and causing the problem of current leakage.Also, crystallization occurs by the heat treatment, by which formationof a transparent insulator is made impossible. That is, by adding one orboth of SnO₂ and SnO to be contained in the glass as its essentialcomponents, the insulator can be provided with both the sealing propertyand transparency. In order to prevent excessive bubbling from occurring,the amount of SnO₂ or SnO to be added may be 1 wt % or more. However,when the content is less than 4.2 wt %, micro bubbles are generated. Asa result, microcracks are generated in the insulator when subjected to atemperature cycle test. On the other hand, when the content is more than20 wt %, since the glass transition point of the glass compositionrises, it does not melt at 577° C. and fails to fill the spaces amongthe crystalline semiconductor particles 2. Judging from the above, thecontent of SnO₂ and/or SnO may be in the range of 4.2 to 20 wt %.

[0102] In addition, a material with a thermal expansion coefficient of40×10⁻⁷ to 80×10⁻⁷/° C. at the temperature range of 40 to 400° C. isused for the insulator 3. Thermal expansion coefficients less than40×10⁻⁷/° C. are so different from the thermal expansion coefficient ofthe substrate 1 comprising aluminum whose thermal expansion coefficientis 240×10⁻⁷/° C. that cracking occurs on the surface of the insulator 3after the formation thereof. Thermal expansion coefficients more than80×10⁻⁷/° C. are so different from that of the crystalline semiconductorparticles 2, which is, for instance, the thermal expansion coefficientof Si:26×10⁻⁷/° C., that cracking occurs in the crystallinesemiconductor particles 2 and the insulator 3 around them. A moredesirable range for the thermal expansion coefficient is 75×10⁻⁷/° C. orless, the optimal range is 70×10⁻⁷/° C. or less at the temperature rangeof 40 to 400° C.

[0103] In cases where the glass transition point of the glass materialis higher than 515° C., the material does not melt at temperaturesaround 577° C., which are the temperatures for joining the substrate 1and the crystalline semiconductor particles 2, failing to fill thespaces among the crystalline semiconductor particles 2, consequentlyfailing to function as an insulator. The glass transition point ispreferably 515° C. or below, in particular, 510° C. or below.

[0104] In this invention, it is preferable that the glass compositionfor the insulator 3 contains components, namely, 4.2 to 20 wt % one orboth of SnO₂ and SnO, 25 to 55 wt % B₂O₃, 20 to 50 wt % ZnO, 3 to 15 wt% Al₂O₃, 2 to 20 wt % SiO₂, and 0.5 to 8 wt % alkali metal oxide, inwhich the weight percentage of the total amount of B₂O₃ and SiO₂ is 35to 70 wt %, as well as the weight percentage of the total amount of allthe components is 90 wt % or more.

[0105] B₂O₃ is a glass network former, as well as lowers the glasstransition point and the thermal expansion coefficient. When the contentof B₂O₃ is below the range of 25 to 55 wt % mentioned above,vitrification becomes hard and also it becomes hard to keep the glasstransition point and thermal expansion coefficient within the abovestated ranges. When the B₂O₃ content is above the aforementioned range,the water resistance deteriorates, which may cause the transparency tobe lost after long time use. A particularly preferred range of the B₂O₃content is 28 to 50 wt %, and the optimum range thereof is 30 to 45 wt%.

[0106] ZnO is a component for lowering the glass transition point andthe thermal expansion coefficient. When the content of ZnO is below therange of 20 to 50 wt % stated above, the thermal expansion coefficientrises to exceed 80×10⁻⁷/° C. On the other hand, when the ZnO content isabove the aforementioned range, vitrification becomes hard. A moredesirable range of the ZnO content is 20 to 50 wt %, and the optimumrange thereof is 30 to 39.5 wt %.

[0107] Al₂O₃ has a function to increase the stability of glass and afunction to lower the thermal expansion coefficient. When the Al₂O₃content is below the range of 3 to 15 wt % stated above, not onlyvitrification becomes hard, but also the thermal expansion coefficientrises to exceed 80×10⁻⁷/° C. When Al₂O₃ content is above theaforementioned range, the glass transition point becomes too high. Amore desirable range of the Al₂O₃ content is 3.5 to 12 wt %, and theoptimum range thereof is 4 to 10 wt %.

[0108] SiO₂ is a glass network former and functions to lower the thermalexpansion coefficient. When the content of SiO₂ is below the range of 2to 20 wt % stated above, vitrification becomes hard, and the thermalexpansion coefficient rises to exceed 80×10⁻⁷/° C. On the other hand,when the SiO₂ content is above the aforementioned range, the glasstransition point becomes too high. A more desirable range of the SiO₂content is 3 to 17 wt %, and the optimum range thereof is 5 to 15 wt %.

[0109] Alkali metal oxides, especially at least one of Li₂O, Na₂O, K₂Oare components for lowering the glass transition point. When the weightpercentage of the total amount of these components is below the range of0.5 to 8 wt % stated above, it becomes very difficult to make the glasstransition point 515° C. or below. In addition, these components alsohave a function to raise the thermal expansion coefficient and afunction to facilitate crystallization of glass. When the weightpercentage of the total amount of these components is above theaforementioned range, the thermal expansion coefficient becomes toohigh, and crystallization occurs during the heat treatment. A moredesirable range of the content of the alkali metal oxides is 0.8 to 7 wt%, and the optimum range thereof is 1 to 6 wt %.

[0110] B₂O₁ and SiO₂ are glass network farmers. When the weightpercentage of the total amount of these components is less than 35 wt %,vitrification becomes hard, and even if the cooling rate is increased soas to make vitrification possible, the tendency toward crystallizationbecomes significant. As a result, the material is crystallized in theinsulating coating formation process. On the other hand, when thecontent is larger than 70 wt %, it becomes impossible to keep the glasstransition point and thermal expansion coefficient within the abovestated ranges. A more desirable range for the weight percentage of thetotal amount of B₂O₃ and SiO₂ is 38 to 65 wt %, and the optimum rangethereof is 40 to 60 wt %.

[0111] A specific range, 90 wt % or more, is selected for the weightpercentage of the total amount of all the above listed components. Thisis because when the content of the above components is below theaforementioned range, the desired properties cannot be obtained. A moredesirable range for the weight percentage of the total amount of theabove listed components is 95 wt % or more and the optimum range thereofis 97 wt %o or more.

[0112] Meanwhile, arbitrary components other than the above listedcomponents may be contained so long as the properties of the glass staywithin the scope of this invention. For example, ZrO₂, TiO₂, La₂O₃ andthe like may be contained for the purpose of enhancing chemicalresistance, and MgO, CaO, SrO, BaO and the like may be contained forfine control of the thermal expansion coefficient and glass transitionpoint at a weight percentage of 10 wt % or less, more desirably, at aweight percentage of 5 wt % or less, and optimally, at a weightpercentage of 3 wt % or less.

[0113] Example

[0114] A substrate formed by attaching a 50 μm thick aluminum alloylayer onto a stainless steel substrate by cold pressing process wasused. For forming a joining-aide layer, a butyral resin was dissolved inan organic solvent and applied on the substrate by screen-printing orthe doctor blade method.

[0115] On top of them, p-type silicon particles with particle sizes of0.2 to 0.6 mm were supplied several times so that the p-type siliconparticles adhered firmly enough to the joining-aide layer. Then, thesubstrate was tilted to remove extra p-type silicon particles.Thereafter, with the p-type silicon particles being pressed by a certainamount of load and kept still, a heat treatment was performed in theatmospheric air at a temperature above the eutectic temperature 577° C.of aluminum and silicon for 5 to 30 minutes, thereby joining the siliconparticles to the aluminum alloy. In order to form an insulator 3 overthe silicon particles, glass particles for low-temperature firingprepared in the form of paste, which were composed of B₂O₃, ZnO, SiO₂,Al₂O₃, Li₂O, SnO and SnO₂ and had average particle sizes of 0.5 to 5 μm,were applied over the silicon particles so that the glass thicknessafter firing was about half the particle size of the silicon particles2. Then, a heat treatment was carried out at a temperature below theeutectic temperature 577° C. of aluminum and silicon for 5 to 30minutes, thereby forming the insulator 3.

[0116] Through the above-mentioned process, twenty kinds of samples werefabricated by varying the components and contents thereof in theinsulator 3 (Examples 11 to 21, Comparative examples 11 to 19). Thenumber of each sample fabricated was five. In examples 11 to 21, the tinoxide (SnO₂ and SnO) contents in the glass were 4.2 to 20 wt %. PbO wasadded in comparative examples 18 and 19. TABLE 3 Example Comparativeexample* No. 11 12 13 14 15 16 17 18 19 20 21 11 12 13 14 15 16 17 18 19Silicon mm 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.2 0.6 0.3 0.3 0.3 0.30.3 0.3 0.3 0.3 0.3 particle size Glass SiO₂ 4.2 0 3.2 5 12 8 20 5 5 5 50 0.5 1 4 22 4 5 5 5 composition SiO 0 4.2 1 0 0 6 0 0 0 0 0 0 0 0 0 0 00 0 0 (wt %) SiO₂ + 4.2 4.2 4.2 5 12 12 20 5 5 5 5 0 0.5 1 4 22 4 5 5 5SiO B₂O₃ 38 38 38 38 35 35 32 34 31 38 38 46 46 44 38 36 31 50 35 30 ZnO38 38 38 38 33 33 30 38 39 38 39 28 28 29 38 24 42 18 29 20 Al₂O₃ 5 5 55 4 4 4 7 7 5 5 7 7 7 5 4 7 6 9 4 SiO₂ 11 11 11 11 12 12 10 10 10 11 1115 15 15 11 10 7 12 10 7 Li₂O 3.8 3.8 3 4 4 4 8 8 3 3 4 3 5 4 4 4 8 5 24 N₂O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 0 K₂O 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 2 0 0 B₂O₃ + 49 49 49 49 47 47 42 44 41 49 49 61 61 58 49 4638 62 45 37 SiO₂ PbO 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 30 Total100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 Thermal E-7/ 64 65 65 65 64 6483 75 80 85 85 63 63 63 64 63 83 85 62 80 expansion C coefficient GlassC 500 501 500 502 506 506 515 460 452 502 502 493 493 494 498 518 441435 487 473 transition point Melting state ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯◯ X ◯ ◯ ◯ ◯ Crystallization ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ ◯ ◯ ◯Cracking ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — X X ◯ ◯ Bubbling ◯ ◯ ◯ ◯ ◯ ◯◯ ◯ ◯ ◯ ◯ ◯ X X ◯ ◯ — ◯ ◯ ◯ ◯ Appearance ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯— ◯ ◯ Pb Pb after HF dep. dep. cleaning Cracking ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯X X X X — X X ◯ ◯ after 500 cycle test Overall ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ XX X X X X X X X evaluation

[0117] The states of stress-cracking in the silicon particles 2 and theinsulator 3, and the melting state of the insulator 3 forming the layerwere checked for each sample fabricated, the results of which are shownin Table 3. In a later step, the upper surfaces of the p-type siliconparticles 2 were cleaned with hydrofluoric acid aqueous solution (HF:pure water=1:100) for 2 to 5 minutes, and the appearance of each samplewas also observed, the results of which are also shown in Table 3.

[0118] Subsequently, a semiconductor layer 4 comprising a mixture ofn-type crystalline silicon and amorphous silicon was formed over thesilicon particles 2 and the insulator 3 to have a thickness of 300 nm,on which a silicon nitride film as a protective layer 5 was formed tohave a thickness of 600 nm. A patterned electrode was formed in theregion where a part of the protective layer 5 had been removed byetching so that it was connected to the semiconductor layer 4 to serveas the other electrode. These photoelectric conversion devices weresubjected to a temperature cycle test in which a temperature cycle of−40 to 90° C. was repeated 500 times. The samples were also inspectedfor generation of microcracks after the test, the results of which arealso included in Table 3.

[0119] In comparative examples 11 and 12, significant bubbling wasobserved by the naked eye in the interfaces between the siliconparticles 2 and the insulator 3. This may be explained that due to thelow content of tin oxide (SnO₂ and SnO) in the glass composition, whichwas less than 1 wt %, intense reaction occurred between the siliconparticles 2 and the insulator 3.

[0120] In comparative examples 13 and 14, no bubbling was observed bythe naked eye in the interfaces between the silicon particles 2 and theinsulator 3. However, microcracks were generated in the insulator afterthe temperature cycle test. This may be explained that although bubblingwas prevented from being excessive because of the tin oxide (SnO₂ andSnO) content of 1 wt % or more, small reaction could not be suppressedand therefore micro bubbles were generated, from which the microcracksdeveloped.

[0121] In comparative example 15, the insulator 3 did not melt at 577°C. This may be explained that due to the tin oxide (SnO₂ and SnO)content of as high as 22 wt %, the glass transition point rose to 518°C.

[0122] On the other hand, in examples 11 to 17, no bubbling was observedin the interfaces between the silicon particles 2 and insulator 3. Theinsulator 3 was able to fill the spaces among the silicon particles 2,and microcracks were not generated after the temperature cycle test.Good results were obtained in these examples.

[0123] According to Table 3, when the glass transition point was 515° C.or below, the glass particles melted and could fill the spaces among thesilicon particles 2. Therefore, it has been found that preferred glasstransition points are 515° C. or below.

[0124] In comparative examples 16 and 17, due to the thermal expansioncoefficients exceeding 80×10⁻⁷/° C. at temperatures 40 to 400° C.,cracking occurred in the silicon particles 2 and insulator 3. On theother hand, no cracking was observed in examples 11 to 19 where thethermal expansion coefficients were 80×10⁻⁷/° C. or less. Accordingly,it has been found that preferred thermal expansion coefficients are80×10⁻⁷/° C. or less.

[0125] In examples 12, 13 and 16, SnO or a mixture of SnO₂ and SnO werecontained as the tin oxide. The obtained results were similar to thosein examples 11 and 15. Accordingly, it has been found that tin oxide tobe added may be at least one of SnO and SnO₂.

[0126] In comparative examples 18 and 19, when cleaning was performedafter the formation of the insulator 3 by using hydrofluoric acidaqueous solution {HF:pure water=1:100} for 2 to 5 minutes, abnormaldeposition of metal lead (Pb) on the surface of the insulator 3 wasobserved. Due to excessive current leakage, measurement of theconversion efficiency was impossible. On the other hand, abnormal metaldeposition was not observed in examples 11 to 21, and measurements ofconversion efficiency were normally performed. Judging from theseresults, it is preferable not to contain lead oxide (Pb) in the glassmaterial for the insulator 3.

[0127] In examples 20 and 21, the samples were fabricated by varying theparticle size of the silicon particles 2 to 0.2 mm and 0.6 mm. Theobtained results were similar to those in examples 11 to 19.

[0128] Accordingly, it has been verified that a good insulator withstable reliability, which is capable of filling the spaces among thesilicon particles 2 and preventing generation of defects such ascracking, bubbling and abnormal deposition can be formed by the presentinvention. <Third Embodiment (glass composition for coating silicon)>

[0129] A glass composition for coating silicon according to thisinvention is substantially free of PbO, and contains B₂O₃, ZnO, and SnO₂and has a thermal expansion coefficient of 80×10⁻⁷/° C. or less attemperatures of 40 to 400° C. and a glass transition point of 550° C. orbelow.

[0130] Here, “substantially free of PbO” means that the PbO content isat a level that cannot be detected by fluorescent X-ray analyses.Namely, it is about 100 ppm or less, especially 50 ppm or less, or morestrictly, 20 ppm or less.

[0131] SnO₂ is an essential component of B₂O₃—ZnO glass for suppressingreaction between silicon and glass. When SnO₂ is not contained, thefollowing inconveniences arise: the resultant silicon semiconductordevice is unusable; due to the gas resulted from reaction between glassand silicon, bubbling occurs during the formation of the insulatingcoating, generating great defects that result in an inadequate sealingproperty; and crystallization occurs by the heat treatment, making itimpossible to form a transparent insulator. In other words, by employingSnO₂ to be contained in the glass as its essential component, theinsulator can be provided with both the sealing property andtransparency.

[0132] Meanwhile, in cases where the thermal expansion coefficient ofthe glass composition is larger than 80×10⁻⁷/° C., the difference inthermal expansion coefficient between silicon (thermal expansioncoefficient: 20×10⁻⁷/° C. to 40×10⁻⁷/° C.) and the glass is so greatthat, when such glass is used for forming an insulating coating oversilicon, cracking occurs in the silicon or glass and pealing occurs inthe interfaces between the glass and silicon in conjunction with theON/OFF switching of the silicon semiconductor device or temperaturechanges accompanying changes in the outside environment. Furthermore,when the thermal expansion coefficient is particularly great, crackingand pealing mentioned above occur when the insulating coating is cooledafter it is formed by firing, thereby making the manufacturing totallyimpossible. A more desirable range of the thermal expansion coefficientis 75×10⁻⁷/° C. or less, and the optimum range thereof is 70×10⁻⁷/° C.or less at the temperature range of 40 to 400° C.

[0133] In cases where the glass transition point of the glass materialis higher than 550° C., the temperature required for firing, by whichthe glass material is softened and fluidized to form an insulatingcoating, is so high that damage to the silicon semiconductor device isextremely large making it prone to malfunction. A particularly desirablerange of the glass transition point is 530° C. or below, and the optimumrange thereof is 500° C. or below

[0134] In this invention, it is preferable that the glass compositionfor coating silicon contains, namely, 1 to 20 wt % SnO₂, 25 to 55 wt %B₂O₃, 20 to 50 wt % ZnO, 3 to 15 wt % Al₂O₃, 2 to 20 wt % SiO₂ and 0.5to 8 wt % alkali metal oxide, in which the weight percentage of thetotal amount of B₂O₃ and SiO₂ is 35 to 70 wt % as well as the weightpercentage of the total amount of all the components is 90 wt % or more.

[0135] Here, SnO₂ is a component for suppressing reaction betweensilicon and glass as mentioned above. When the SnO₂ content is less than1 wt %, the effect of suppressing reaction becomes insufficient. On theother hand, when the SnO₂ content is more than 20 wt %, it becomes hardto make the glass transition point below 550° C. A more desirable rangeof the SnO₂ content is 2 to 15 wt %, and the optimum range thereof is4.2 to 10 wt %.

[0136] B₂O₃ is a glass network former, as well as it lowers the glasstransition point and the thermal expansion coefficient. When the contentof B₂O₃ is below the range of 25 to 55 wt % stated above, vitrificationbecomes hard and also it becomes hard to keep the glass transition pointand thermal expansion coefficient within the above stated ranges. Whenthe B₂O₃ content is above the aforementioned range, the water resistancedeteriorates, which may cause transparency to he lost after long timeuse. A particularly preferred range of the B₂O₃ content is 28 to 50 wt%, and the optimum range thereof is 30 to 45 wt %.

[0137] ZnO is a component for lowering the glass transition point andthe thermal expansion coefficient. When the content of ZnO is below therange of 20 to 50 wt % stated above, the thermal expansion coefficientrises to exceed 80×10⁻⁷/° C. On the other hand, when the ZnO content isabove the aforementioned 20 to 50 wt % range, vitrification becomeshard. A more desirable range of the ZnO content is 20 to 50 wt %, andthe optimum range thereof is 30 to 39.5 wt %.

[0138] Al₂O₃ has a function to increase the stability of glass and afunction to lower the thermal expansion coefficient. When the Al₂O₃content is below the range of 3 to 15 wt % stated above, not onlyvitrification becomes hard, but also the thermal expansion coefficientrises to exceed 80×10⁻⁷/° C. When the Al₂O₃ content is above theaforementioned 3 to 15 wt % range, the glass transition point becomestoo high. A more desirable range of the Al₂O₃ content is 3.5 to 12 wt %,and the optimum range thereof is 4 to 10 wt %.

[0139] SiO₂ is a glass network former and works to lower the thermalexpansion coefficient. When the content of SiO₂ is below the range of 2to 20 wt % stated above, vitrification becomes hard, and the thermalexpansion coefficient rises to exceed 80×10⁻⁷/° C. On the other hand,when the SiO₂ content is above the aforementioned 2 to 20 wt %, theglass transition point becomes too high. A more desirable range for theSiO₂ content is 3 to 17 wt %, and the optimum range thereof is 5 to 15wt %.

[0140] Alkali metal oxides, especially at least one of Li₂O, Na₂O, K₂Oare components for lowering the glass transition point. When the weightpercentage of the total amount of these components is below the range of0.5 to 8 wt % stated above, it becomes very difficult to make the glasstransition point 550° C. or below. In addition, these components alsohave a function to raise the thermal expansion coefficient and afunction to facilitate crystallization of glass. Accordingly, when theweight percentage of the total amount of these components is above therange of 0.5 to 8 wt % stated above, the thermal expansion coefficientbecomes too high, and crystallization occurs during the heat treatment.A more desirable range of the content of the alkali metal oxides is 0.8to 7 wt %, and the optimum range thereof is 1 to 6 wt %.

[0141] B₂O₃ and SiO₂ are glass network formers. When the weightpercentage of the total amount of these components is less than 35 wt %,vitrification becomes hard, and even if the cooling rate is increased soas to make vitrification possible, the tendency toward crystallizationbecomes significant. As a result, crystallization occurs in theinsulating coating formation process. On the other hand, when it islarger than 70 wt %, it becomes impossible to keep the glass transitionpoint and thermal expansion coefficient within the above stated ranges.A more desirable range of the weight percentage of the total amount ofB₂O₃ and SiO₂ is 38 to 65 wt %, and the optimum range thereof is 40 to60 wt %.

[0142] A specific range, 90 wt % or more, is selected for the weightpercentage of the total amount of all the above listed components. Thisis because when the content of the above components is below theaforementioned range, the desired properties cannot be obtained. A moredesirable range for the weight percentage of the total amount of theabove listed components is 95 wt % or more and the optimum range thereofis 97 wt % or more.

[0143] Meanwhile, arbitrary components other than the above listedcomponents may be contained so long as the properties of the glass staywithin the scope of this invention. For example, ZrO₂, TiO₂, La₂O₃ andthe like may be contained for the purpose of enhancing chemicalresistance, CoO, NiO, Cr₂O₃, Nd₂O₃, MnO, Au, Ag, Cu and the like may becontained for coloration, and MgO, CaO, SrO, BaO and the like may becontained for fine control of the thermal expansion coefficient andglass transition point at a weight percentage of 10 wt % or less, moredesirably, at a weight percentage of 5 wt % or less, or optimally, at aweight percentage of 3 wt % or less.

[0144] Also, in the present invention, it is preferred that the contentof each of As₂O₃ and Sb₂O₃ which are widely used in conventional glass,especially in optical glass as clarifying agents, in the glasscomposition for coating silicon is 0.1 wt % or less. Most desirably, theglass composition for coating silicon does not contain As₂O₃ or Sb₂O₃except for inevitable amount of impurities. The reason for this is thatAs₂O₃ and Sb₂O₃ are toxic substances which are desirably not containedin the glass composition in view of environment friendliness.

[0145] Also, in this invention, it is preferred that reaction gas is notgenerated when a heat treatment is carried out at 600° C. or below afterthe silicon is covered with the glass composition for coating silicon.This is because if some kind of reaction gas is generated by a reactionbetween the silicon and glass during the heat treatment for softeningand fluidizing glass to form an insulating coating over the silicon,bubbles are generated in the insulating coating, creating great defects,by which the coating becomes incapable of protecting silicon andfunctioning as an insulator, and even loses transparency as mentionedlater.

[0146] Also, it is preferred in this invention that the glasscomposition for coating silicon is not crystallized during the heattreatment at a temperature 600° C. or below after covering the surfaceof silicon. This is because if the glass material is crystallized duringthe heat treatment for softening and fluidizing the glass material toform an insulating coating over the silicon, a change in volumeaccompanying the crystallization may change the thermal expansioncoefficient causing it to deviate from the desired range, and also thetransparency may be lost.

[0147] In addition, it is preferred in this invention that the glasscomposition for coating silicon is capable of forming a substantiallytransparent glass coating by being subjected to a heat treatment at 600°C. or below after covering the surface of silicon. This is because ifthe insulating coating is not transparent after the heat treatment forsoftening and fluidizing the glass material to form an insulatingcoating, it is impossible to use such a coating especially as aninsulating coating for optical sensors or solar cells.

[0148] <Fourth Embodiment (insulating coating in contact with silicon)>

[0149] Now, an insulating coating in contact with silicon according tothis invention is described.

[0150] The insulating coating comprises a glass which is substantiallyfree of PbO, and contains B₂O₃, ZnO and SnO₃, and has a thermalexpansion coefficient of 80×10⁻⁷/° C. or less at temperatures of 40 to400° C., and a glass transition point of 550° C. or below.

[0151] The insulating coating comprising glass may be fabricated bycovering a surface of silicon with a glass powder which is substantiallyfree of PbO, and contains B₂O₂, ZnO and SnO₂, and has a thermalexpansion coefficient of 80×10⁻⁷/° C. or less at temperatures of 40 to400° C. and a glass transition point of 550° C. or below, and performinga heat treatment at 600° C. or below to soften and fluidize the glasspowder.

[0152] Meanwhile, when the temperature for the heat treatment is higherthan 600° C., damage by heat to the silicon semiconductor device becomesso great that the rate of defective devices increases, lowering theyield and making the devices prone to malfunction. A more desirabletemperature range for the heat treatment is 580° C. or below, and theoptimum temperature range for it is 570° C. or below. In addition, inorder to reduce damage by heat to the silicon semiconductor device, thetime of the heat treatment is preferably one hour or less, moredesirably, 50 minutes or less, and optimally, 45 minutes or less.

[0153] Additionally, in the present invention, it is preferred that thediameter of the largest bubble contained in the insulating coating incontact with silicon is 1 mm or less, and the number of bubbles eachhaving a diameter of 0.1 mm or more is not more than twenty in 1 cm².

[0154] This is because when the diameter of the largest bubble is largerthan 1 mm, defects in the insulating coating are so great that thesealing property for protecting the silicon semiconductor device isdeteriorated and the transparency is lost. When the number of bubbleseach having a diameter of 0.1 mm or more exceeds twenty in 1 cm², theinsulating coating fails to have transparency.

[0155] Here, a more desirable range of the diameter of the largestbubble is 0.5 mm or less, and optimally, it is 0.2 mm or less. Inaddition, a more desirable range of the number of bubbles each having adiameter of 0.1 mm or more is not more than ten in 1 cm², and optimally,it is not more than five in 1 cm².

[0156] In the present invention, it is necessary that the aforementionedinsulating coating in contact with silicon is substantially transparentwhen it is used as an insulating coating for optical sensors and solarcells. This is because if such an insulator coating is not transparent,light is not transmitted through it and the device loses its primaryfunction.

[0157] Moreover, it is preferred in this invention that the averageparticle size of the aforementioned glass powder is 50 μm or less. Whenthe average particle size of the glass powder is more than 50 μm, thefluidity of the glass powder deteriorates, the time required for theheat treatment for forming a transparent, defect-free insulating coatingis therefore prolonged. As a result, damage by heat to the siliconsemiconductor device becomes too great. In addition, spaces amongparticles in an initial stage are so large that it is difficult to fillthe spaces by softening and fluidizing of the powder. A more desirablerange of the average particle size is 30 μm or less, and optimally, itis 20 μm or less.

[0158] Furthermore, it is preferred in this invention that theaforementioned glass powder is a mixture of two or more different kindsof glass powders having different average particle sizes. This isbecause when the glass powder is supplied to the silicon surface, bymixing glass powders with two or more different particle sizes togetherat an appropriate ratio in which coarse powder is mixed with smallersize powder that fills spaces among the coarse powder, the powderpacking density is enhanced. Shrinking of the glass during the firingcan be thus suppressed to a minimum, facilitating control of thethickness and shape of the insulating coating, and improving the yield.

[0159] As one example of products employing the insulating coating incontact with silicon described above, a preferred example, an opticalsensor, is now described referring to FIG. 3 that shows a schematiccross section thereof.

[0160] In FIG. 3, there is provided a pack-age A comprising aninsulating substrate 21 made from ceramics or the like, a wiring layer22 including metallization layers and via hole conductors, and terminalelectrodes 23. A cavity 24 is formed in a central portion of the uppersurface of the package A. Inside the cavity 24, a silicon optical sensordevice 25 is bonded to be fixed to the insulating substrate 21 throughan adhesive (not shown) made of glass or wax or the like. The siliconoptical sensor device 25 is electrically connected to the wiring layer22 through bonding wires 26 and the like. The surfaces of the siliconoptical sensor 25 are sealed with an insulating coating 27.

[0161] The insulating coating 27 has a low glass transition point and alow thermal expansion coefficient, and does not react to silicon, aswell as it is transparent and not crystallized in the desiredtemperature range. Accordingly, even when the silicon optical sensordevice 25 is a large scale device, occurrence of cracking and peelingcan be prevented over a long period of time, and therefore the siliconoptical sensor device 25 can be sealed and protected over a long periodof time.

[0162] In order to form such an insulating coating in contact withsilicon as mentioned above, specifically, an appropriate organic binder,dispersaent, solvent are added to the glass powder mentioned above andmixed together so as to prepare glass paste. A package on which asilicon semiconductor device has previously been mounted is prepared,and the glass paste is supplied in a required amount to the area thatneeds to be coated by one of the various conventionally known printingmethods, a dipping process, a dispensing process, spin coating, lowpressure impregnation or the like. Incidentally, it is not necessary tosupply the glass paste to areas on a silicon semiconductor device,especially areas in a large scale silicon semiconductor device such as asolar cell that do not need to be coated with the insulating coating.

[0163] Subsequently, after extra solvent and the like are removed bydrying, binder removal is carried out in an oxidizing atmosphere or alow oxidizing atmosphere. Thereafter, firing is carried out at atemperature of 600° C. or below in an oxidizing or non-oxidizingatmosphere to soften and fluidize the glass powder, thereby forming theinsulating coating in contact with silicon of the present invention onthe silicon semiconductor device.

[0164] Example A

[0165] A prescribed amount of metal oxide powders or metal carbonatepowders were used as the material. They were weighed and mixed together,and the powder mixture was melted in a platinum crucible in anatmospheric air at 1200 to 1400° C. for 2 hours. The resultant melt wasrapidly cooled by pouring it onto an iron plate, thereby fabricatingbulk bodies of glass having the compositions shown in Table 4. TABLE 4Sample No. *31 32 33 34 35 36 *37 38 39 40 41 42 43 44 *45 *46 GlassSnO₂ 0 3 5 7 9 13 21 4 6 5 5 5 9 5 5 4 composition B₂O₃ 44 43 42 43 4241 36 31 32 31 36 32 37 38 50 31 (wt %) ZnO 29 28 28 28 27 26 24 42 3839 41 38 36 37 18 42 Al₂O₃ 7 7 6 5 5 4 4 7 7 7 9 4 4 5 6 7 SiO₂ 15 14 1413 13 12 10 12 13 10 4 17 6 7 10 7 Li₂O 4 4 4 4 4 4 4 4 4 6 2 4 4 4 4 8Na₂O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 K₂O 0 0 0 0 0 0 0 0 0 0 0 0 1 1 2 0B₂O₃ + SiO₂ 59 57 56 56 55 53 46 43 45 41 40 49 43 45 60 38 Sub total 9999 99 100 100 100 99 100 100 98 97 100 97 97 97 100 ZrO₂ 1 1 0 0 0 0 1 00 0 2 0 2 2 1 0 TiO₂ 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 0 CoO 0 0 0 0 0 0 0 00 2 0 0 1 0 0 0 Nd₂O₃ 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 Total 100 100 100100 100 100 100 100 100 100 100 100 100 100 100 100 Vitrification ◯ ◯ ◯◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Thermal E-7/° C. 63 64 64 66 66 65 63 64 62 7260 66 68 69 85 83 expansion coefficient Glass ° C. 480 482 485 489 499527 554 488 485 459 515 501 495 488 432 441 transition point HT °C. 550550 550 560 570 590 610 560 570 530 580 580 570 570 510 510 temperatureHT time Min. 15 15 15 15 15 15 30 15 15 15 30 15 15 15 15 15Crystallization ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Diameter of mmm 15 0.50.4 0.4 0.3 0.3 0.3 0.3 0.4 0.5 0.4 0.8 0.3 0.6 0.5 0.6 largest bubbleNumber of N/cm² 42 10 7 5 4 2 1 6 6 6 5 9 5 9 8 7 bubbles TransparencyInitial X ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ X ◯ stage After 500 — ◯ ◯ ◯ ◯ ◯ ◯ ◯◯ ◯ ◯ ◯ ◯ ◯ — X cycle test

[0166] Each of the bulk bodies of glass was processed into a prismaticshape of 4×4×15 mm in size, and the thermal expansion coefficient attemperatures 40 to 400° C. was measured by using a thermomechanicalanalyzer for each sample. The obtained results are shown in Table 4.

[0167] Subsequently, the glass was crushed in a ball mill so that theparticles have average particle sizes of 5 μm and 0.5 μm. At this stage,the glass transition point of the powder with an average particle sizeof 5 μm was measured with a differential scanning calorimeter (DSC) andfurthermore, vitrification was checked by using an x-ray diffractionanalyzer, where samples that did not show crystalline diffractionpatterns were marked by ◯ (good), samples that showed crystallinediffraction patterns were marked by X (defective), the results of whichare shown in Table 4.

[0168] Then, the two kinds of glass powders having different averageparticle sizes were weighed so that the weight ratio between them was “5μm average particle size glass/0.5 μm average particle sizeglass=70/30”, and an organic binder, a dispersant and a solvent wereadded to the mixture and mixed together to prepare glass paste.

[0169] Meanwhile, polycrystalline silicon substrates used for solarcells and the like were prepared for evaluation purpose, which had beenpreviously cut into 1 cm pieces.

[0170] Then, the aforementioned glass paste was applied to each of thesilicon substrates for evaluation to have a thickness of 100 μm by adispensing process, and dried so as to evaporate extra solvent, andthereafter subjected to a heat treatment in the atmospheric air with theconditions shown in Table 4.

[0171] The obtained insulating coatings for coating silicon formed onthe silicon substrates were inspected on whether they had crystallinephases or not by an x-ray diffraction analysis, where samples that didnot show crystalline diffraction patterns were marked by ◯ (good), andsamples that showed crystalline diffraction patterns were marked by ×(defective) The obtained results are shown in Table 4. Also, photographsof the insulating coatings were taken with a CCD camera, and thediameter of the largest bubble and the number of bubbles each having adiameter larger than 0.1 mm in 1 cm² area were measured for each sample,the results of which are shown in Table 4. Here, samples in which thediameter of the largest bubble was larger than 1 mm and samples in whichthe number of bubbles with diameters of 0.1 mm or more was more than 20in 1 cm² area were evaluated as defective.

[0172] Also, in an evaluation of transparency by the naked eye, samplesin which the grain boundaries of the polycrystalline silicon substrateswere viewable through the insulating coatings were marked by ◯ (good),while samples in which they were not viewable were marked by ×(defective).

[0173] Furthermore, a temperature cycle test was carried out, in whichthe insulating coatings formed on the silicon substrates for evaluationwere disposed alternately in thermostatic ovens whose temperatures werekept at 0° C. and 80° C. in the ambient atmosphere, and the samples werekept in each of the ovens for 15 minutes, which was determined as onecycle. Five hundred cycles were performed in the temperature cycle test.After the test, the silicon substrates and/or insulating coatings wereinspected on the presence or absence of cracking and peeling. Samples inwhich no cracking or peeling occurred were marked by ◯ (good), andsamples in which cracking or peeling occurred were marked by ×(defective).

[0174] As is apparent from the results shown in Table 4, in samples No.32 to 36, 38 to 44 based upon the present invention had thermalexpansion coefficients of less than 80×10⁻²/° C. at the temperaturerange of 40 to 400° C., and glass transition points of less than 500° C.They did not emit gas due to reaction to silicon, and were notcrystallized, resulting in transparent insulating coatings. In addition,they did not suffer cracking or peeling even after the temperature cycletest, good insulating coatings were therefore formed on the surfaces ofthe silicon.

[0175] On the other hand, in sample No. 31 which did not contain SnO₂,glass and silicon reacted to each other generating many large bubbles.As a result, a transparent insulating coating was not formed in sample31. In sample No. 37 where the SnO₂ content was larger than 20 wt %, theglass transition point was higher than 550° C. As a result, formation ofan insulating coating was impossible by the heat treatment at atemperature below 600° C. In addition, in samples No. 45, 46 in whichthe thermal expansion coefficients were larger than 80×10⁻⁷/° C.,cracking and peeling occurred after the 500 cycle-temperature cycletest. The samples were of the quality that is incapable of securing longtime reliability.

[0176] Example B

[0177] An optical sensor apparatus with a silicon optical sensor devicemounted on an alumina package was prepared. Glass paste was formed byusing the glass powder in sample No. 33 shown in Table 4 in the same wayas in Example A, and an insulating coating was formed on the opticalsensor device by the same process.

[0178] When the operation of the optical sensor apparatus was examined,it exhibited good properties of sensor. Also, its performance did notchange after the 500 cycle-temperature cycle test similar to the abovementioned one.

1. A photoelectric conversion device comprising: a metal substrate or asubstrate having a metal layer formed on a surface thereof; numerousfirst conductivity-type crystalline semiconductor particles deposited onthe substrate; an insulator provided among the numerous firstconductivity-type crystalline semiconductor particles; and a secondconductivity-type semiconductor region formed on upper portions of thefirst conductivity-type crystalline semiconductor particles, wherein thecrystalline semiconductor particles comprise silicon, and the insulatorcomprises a glass material which contains at least 1 wt % and at most 20wt % tin oxide.
 2. The photoelectric conversion device according toclaim 1, wherein the insulator has a thermal expansion coefficient of30×10⁻²/° C. to 65×10⁻²/° C. at temperatures of 30 to 300° C.
 3. Thephotoelectric conversion device according to, claim 1, wherein theinsulator has a glass transition point of 560° C. or below.
 4. Thephotoelectric conversion device according to claim 1, wherein the metalof the metal substrate or the metal layer comprises aluminum.
 5. Thephotoelectric conversion device according to claim 1, wherein thecrystalline semiconductor particles have an average particle size of 0.2mm to 0.6 mm.
 6. The photoelectric conversion device according to claim1, wherein the insulator is substantially free of lead oxide.
 7. Aphotoelectric conversion device comprising: a metal substrate or asubstrate having a metal layer formed on a surface thereof; numerousfirst conductivity-type crystalline semiconductor particles deposited onthe substrate; an insulator provided among the numerous firstconductivity-type crystalline semiconductor particles; and a secondconductivity-type semiconductor region formed on upper portions of thefirst conductivity-type crystalline semiconductor particles, wherein thecrystalline semiconductor particles comprise silicon, and the insulatorcomprises a glass composition which contains 4.2 wt % to 20 wt % tinoxide.
 8. The photoelectric conversion device according to claim 7,wherein the insulator has a thermal expansion coefficient of 40×10⁻⁷/°C. to 80×10⁻⁷/° C. at temperatures of 40 to 400° C.
 9. The photoelectricconversion device according to claim 7, wherein the insulator has aglass transition point of 515° C. or below.
 10. The photoelectricconversion device according to claim 7, wherein the insulator comprisesa glass composition which contains 4.2 to 20wt % at least one of SnO andSnO₂, 25 to 55 wt % B₂O₃, 20 to 50 wt %, ZnO, 3 to 15 wt % Al₂O₃, 2 to20 wt % SiO₂, and 0.5 to 8 wt % alkali metal oxide, in which the weightpercentage of the total amount of B₂O₃ and SiO₂ is 35 to 70 wt %, andthe weight percentage of the total amount of all the components is 90 wt% or more.
 11. The photoelectric conversion device according to claim 7,wherein the metal of the metal subsbtrate or the metal layer comprisesaluminum.
 12. The photoelectric conversion device according to claim 7,wherein the crystalline semiconductor particles have an average particlesize of 0.2 mm to 0.6 mm.
 13. A glass composition for coating siliconwhich is substantially free of PbO, and contains B₂O₃, ZnO and SnO₂, andhas a thermal expansion coefficient of 80×10⁻⁷/° C. or less attemperatures of 40 to 400° C. and a glass transition point of 550° C. orbelow.
 14. The glass composition for coating silicon according to claim13, wherein the glass composition contains 1 to 20wt % SnO₂.
 15. Theglass composition for coating silicon according to claim 13, wherein theglass composition further contains SiO₂, Al₂O₃, and an alkali metaloxide.
 16. The glass composition for coating silicon according to claim13, wherein the glass composition contains 1 to 20 wt 2 SnO₂, 25 to 55wt % B₂O₃, 20 to 50 wt % ZnO, 3 to 15 wt % Al₂O₂, 2 to 20 wt %, SiO₂,and 0.5 to 8 wt % alkali metal oxide, in which the weight percentage ofthe total amount of B₂O₂ and SiO₂ is 35 to 70 wt %, and the weightpercentage of the total amount of all the components is 90 wt % or more.17. The glass composition for coating silicon according to claim 13,wherein the content of each of As₂O₃ and Sb₂O₃ is 0.1 wt % or less. 18.The glass composition for coating silicon according to claim 13, whereinreaction gas is not generated during a heat treatment at a temperatureof 600° C. or below that is performed after the glass composition hascovered a surface of the silicon.
 19. The glass composition for coatingsilicon according to claim 13, wherein the glass composition is notcrystallized during a heat treatment at a temperature of 600° C. orbelow that is performed after the glass composition has covered asurface of the silicon.
 20. The glass composition for coating siliconaccording to claim 13, wherein the glass composition is capable offorming a substantially transparent glass coating by being subjected toa heat treatment at a temperature of 600° C. or below that is performedafter the glass component has covered a surface of the silicon.
 21. Aninsulating coating comprising a glass composition which is substantiallyfree of PbO, and contains B₂O₃, ZnO and SnO₂, and has a thermalexpansion coefficient of 80×10⁻⁷/° C. or less at temperatures of 40 to400° C. and a glass transition point of 550° C. or below, the insulatingcoating being formed on a part of or the whole surface of silicon in asemiconductor device.
 22. The insulating coating according to claim 21,wherein the glass composition constituting the insulating coatingcontains 1 to 20 wt % SnO₂.
 23. The insulating coating according toclaim 21, wherein the glass composition constituting the insulatingcoating further contains SiO₂, Al₂O₃ and an alkali metal oxide.
 24. Theinsulating coating according to claim 21, wherein the glass compositionconstituting the insulating coating contains 1 to 20 wt % SnO₂, 25 to 55wt % B₂O₃, 20 to 50 wt % ZnO, 3 to 15 wt % Al₂O₃, 2 to 20 wt % SiO₂, and0. 5 to 8 wt % alkali metal oxide, in which the weight percentage of thetotal amount Of B₂O₃ and SiO₂ is 35 to 70 wt %, and the weightpercentage of the total amount of all the components is 90 wt % or more.25. The insulating coating according to claim 21, wherein the content ofeach of As₂O 2 and Sb₂O₃ in the glass composition constituting theinsulating coating is 0.1 wt % or less.
 26. The insulating coatingaccording to claim 21, wherein the diameter of the largest bubble in theglass composition constituting the insulating coating is 1 mm or less,and the number of bubbles each having a diameter of 0.1 mm or more inthe glass composition constituting the insulating coating is 20 or lessin 1 cm₂ area.
 27. The insulating coating according to claim 21, whereinthe glass composition constituting the insulating coating issubstantially transparent.
 28. A method of forming an insulating coatingcomprising the steps of: covering a surface of silicon with a glasspowder which is substantially free of PbO, and contains B₂O₃, ZnO andSnO₂, and has a thermal expansion coefficient of 8×10⁻⁷/° C., or less attemperatures of 40 to 40020 C. and a glass transition point of 550° C.or below; and performing a heat treatment at a temperature of 600° C. orbelow for softening and fluidizing the glass powder, whereby forming aninsulating coating on the silicon.
 29. The method of forming aninsulating coating according to claim 28, wherein the glass powder hasan average particle size of 50 μm or less.
 30. The method of forming aninsulating coating according to claim 28, wherein the glass powder is amixture of two or more kinds of glass powders each having an averageparticle size that is different from one another.
 31. A semiconductordevice including silicon therein which is partly or wholly coated withan insulating coating comprising a glass composition which issubstantially free of PbO, and contains B₂O₃, ZnO and SnO₂, and has athermal expansion coefficient of 80×10⁻⁷/° C. or less at temperatures of40 to 400° C. and a glass transition point of 550° C. or below.